A problem in the use of robots in tooling operations is the problem of overload on the robot arm. This may occur if the robot arm or tool collides with something or if the tool gets stuck in the workpiece.
Several devices have been proposed and are in use that detect stresses and overloads on the robot arm and immediately shut down the robot when overload is detected in order to avoid damage to the robot or to the workpiece. These devices include expandable breakaway joints and connectors that break away when the robot arm experiences an overload.
For example, the devices shown in our U.S. Pat. Nos. 4,717,003 and 4,848,546 are expandable clutches useful in most robotic tooling situations. It has been found, however, that a collapsible clutch is preferable for use when the tool is an arc welding electrode, as collisions with the work piece are a more common occurrence. An expandable clutch as shown in our previous patents may not trip at a low enough threshold to protect the welding torch from damage if a collision puts the clutch into a compression failure mode. It has also been found that the ball and socket type of connection utilized in our expandable clutches is inappropriate for use in a collapsible clutch due to excessive friction between the parts, causing nonrepeatability.